It is customarily desired that the piston in hydraulic equipment maintains its assumed position without moving when one or more valves are closed. The necessary preconditions to satisfy this situation are: noncompressible hydraulic mediums, conduits and vessels of unchanging volume, the absence of air and vapor in the space filled with hydraulic liquid and delimited by the piston. Impact loads acting upon the piston in its direction of movement are absorbed by the abrupt pressure increase of the hydraulic liquid and by the elastic deformation of the metal component parts. The resulting spring characteristic line of this hydraulic equipment is very steep and is virtually unnoticed by the rider.
U.S. patent application Ser. No. 08/740,350, filed Nov. 8, 1996, discloses a saddle support for bicycles which can be positioned hydraulically. In this way, saddles, with and without spring suspension, which are attached to a saddle support operating as a piston, can be positioned at the height required for ergonomic and safety reasons. However, impact loads caused by the ground surface and transmitted to the seat and spine of the rider via the bicycle cannot be absorbed in addition to those already absorbed by the tires and the suspension of the saddle. As can be seen in many devices available in the marketplace, additional shock absorption is desirable in bicycles equipped with tires of small diameter and saddles which are not spring suspended as well as for travel over an uneven road surface.